Microbes in Human Welfare — Part 2: Sewage, biogas, biocontrol and biofertilisers: visual lesson, ISC Class 12 Biology

Lesson

Microbes for a cleaner environment

Part 2 — microbes that clean sewage, make fuel, control pests and feed crops.

In this lesson you will

Describe primary and secondary treatment of sewage and the meaning of BOD
Describe methanogens, the composition of biogas and the working of a biogas plant
Explain biocontrol, integrated pest management, the harm of chemical pesticides, and biofertilisers

Diagram

Sewage treatment

Primary treatment is physical: floating debris is removed by filtration, and grit and soil by sedimentation, leaving primary sludge. Secondary (biological) treatment: the effluent is aerated, and aerobic microbes grow as flocs — masses of bacteria with fungal filaments — that consume organic matter.

Diagram

Biochemical oxygen demand

BOD is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. The higher the BOD, the more polluting the water.

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